http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V3H-4829HKJ-JP-1&_cdi=5731&_user=1913507&_orig=search&_coverDate=07%2F31%2F1984&_sk=999729992&view=c&wchp=dGLbVtz-zSkWz&md5=1e18cdac5ba935fa9d948afbf3e79c9e&ie=/sdarticle.pdf